South Platte Master Plan — a stream corridor evaluation – is complete

The Platte River is formed in western Nebraska east of the city of North Platte, Nebraska by the confluence of the North Platte and the South Platte Rivers, which both arise from snowmelt in the eastern Rockies east of the Continental Divide. Map via Wikimedia.

High Plains in eastern Colorado. Photo credit Bob Berwyn.

The plains around DIA were parched by the scorching 2012 drought, although groundwater pumping along the South Platte River enabled some farms to continue irrigating — photo by Bob Berwyn

Map of the South Platte River alluvial aquifer subregions — Colorado Water Conservation Board via the Colorado Water Institute

The South Platte Master Plan is a study of flood mitigation and recovery possibilities along 130 miles of the South Platte River from the Morgan-Weld county line to the Nebraska State Line. Authorized and funded by the Colorado Department of Local Affairs, the plan will suggest ways to make the river more “flood resilient,” both to handle the flooding as it occurs, with minimal damage to property and structures, and to quickly recover from a flood in the aftermath.

Five big problem areas were identified in the evaluation, according to Brian Murphy, project director for CDM Smith of Denver, the contractor on the flood study. They were the amount of sediment the floods of 2013 and 2015 deposited in the study area, basically clogging the river and making flooding worse; uncontrolled water in ditches and canals, which can back up and cause damage to structures, homes, and fields; the railroad railroad right of way southwest of Messex, which contains the river along the northwest shoreline but worsens flooding on the opposite shoreline; the hunting lands along the river that provide game habitat but also blocks water flow during a flood, causing the water to spread out into neighboring cropland; and the washed-out headgates of the Henderson-Smith and Lowline ditches, which essentially turn those ditches into another channel of the river.

Stakeholders attending the meeting may have gotten some ideas of how to tackle those challenges from a 90-minute presentation by Jerry Kenny, executive director of the Platte River Recovery Implementation Program. That program comes from an agreement among Colorado, Nebraska, Wyoming, and the U.S. Department of the Interior to preserve habitat for whooping cranes, least terns, piping plovers and pallid sturgeons, four species on the endangered species list. The program maintains water at an adequate level along an 80-mile stretch of the Platte River the Nebraska cities of Lexington and Grand Island in an area call the Big Bend Area.

Kenny’s description of challenges faced in maintaining habitat for those four species brought home to the stakeholders how the river system has been affected by settlement all along its length. For instance, sediment – mostly sand – that once washed downstream past what is now Sterling and settled in the Big Bend area to create habitat for those species no longer makes it that far. Instead, repeated diversion of the river for irrigation reduces and slows down the water flow during what was once rapid spring runoff, depositing the sediment here.

That problem is exacerbated by Lake McConaughy on the North Platte near Ogallala, which traps sediment that once drifted down into Big Bend.

Kenny told the meeting that some of the challenges have been met by practices in all three of the states that have increased stream flow in the Platte River. Most notable in Colorado is the Tamarack Recharge Project near Crook, in which water is pumped into small reservoirs when there is no irrigation demand on the river, and allowed to seep back into the river so more water is available downstream.

Kenny also showed the group slides of off-stream water storage projects that have been used to create wetlands and much-needed sand islands in the project area. Presumably, some of those ideas could be used to mitigate flooding and provide some off-channel water storage in the South Platte basin as well.

After the meeting Morgan County Commissioners Jim Zwetzig and Laura Teague said they are encouraged by the “collaborative effort” shown in the PRRIP agreements…

Project manager Brian Murphy said one of the biggest challenges, once ideas and practices are identified, will be finding the dollars to do it. The PRRIP get about half of its funds from the federal government, and there is tremendous incentive in the form of a mandate to save endanger species. There is no such incentive, other than reducing unpredictable costs of recover, in flood mitigation.

“The big question is, what are the things that can bring dollars to fund this project,” Murphy said. “What are the drivers? There’s been a lot of discussion of duck habitat, open space, trails, and I think it’s going to come down to those things.”

On a more positive note, he said, the PRRIP process has broken new ground when working with the federal permitting process. Some of the techniques that project uses, such as tilling riparian areas to keep vegetation down, are considered agricultural, and so don’t need federal permits.

Monday’s meeting was the third since the plan was introduced to the public in February.